Prior art of interest is Grossman, U.S. Pat. No. 2,941,832 for Sliding Door Lock and Adickes, U.S. Pat. No. 3,837,693 for Locks for Sliding Members.
A sliding vent, such as a door or window, is generally provided with a lock in the central portion of the lock stile thereof to immobilize the door or window. Although these primary locks provide a certain amount of security, clever thieves have learned how to open them; and while the market place and the patent literature afford numerous types of back-up devices, there is still considerable room for improvement.